Manufacturing processes whereby catalyst compositions are precipitated using an alkaline precipitant are known and typically include the steps of forming an aqueous, often an acidic solution of metal compounds, combining the solution with an alkaline precipitant, generally an aqueous solution of one or more of an alkali metal carbonate, alkali metal bicarbonate, alkali metal hydroxide, ammonium carbonate or ammonium hydroxide, to effect precipitation of insoluble metal compounds. The insoluble compounds may be aged for a period in the slurry phase. The aged slurry is then filtered to recover the catalyst composition and dried. Calcination, whereby the dried catalyst composition is heated to elevated temperature to effect a physiochemical change may also be performed. Furthermore, for certain reducible catalyst compositions, for example those comprising Ni, Cu, Co or Fe, the dried or calcined materials may subsequently be exposed to a reducing gas such as hydrogen or carbon monoxide to convert the metal into its elemental or zero-valent state. Subsequent passivation of the reduced catalyst composition may also be performed.
Precipitation is a very rapid process and a subsequent ageing step allows the initially formed precipitate to transform into desired phases and/or morphologies, e.g. a desired crystallite size. Ageing is typically carried out in a batch or semi-continuous procedure whereby the aqueous slurry of precipitated metal compounds is held at elevated temperatures in one or more stirred vessels for selected periods of time. Continuous processes typically employ a number of stirred tanks in series. Such procedures have been used although they can be difficult to control and are therefore prone to give undesirable product variation. Despite this, the development of a suitable single stage continuous process has not been heretofore successful.